As technology pushes towards sub-micrometer and deep sub-micrometer applications, the speed performance ushers in the requirements of thicker inter-layer dielectric (ILD) for lowering of intra-connects capacitance and hence has resulted in higher aspect ratio for the contacts and vias. Higher current driving capability also requires a highly reliable metalization both in the horizontal and vertical direction. Metal step coverage is one of the key factors that affects the reliability of metalization.
In order to enhance the step coverage and hence reliability, technologists have proposed chemical vapor deposition (CVD) metalization technology, notably selective tungsten and tungsten plug (with etch back), to provide a solution to the problem. These are workable solutions, but suffer from high cost of manufacturing, added complexity and are prone to high particulate generation.
Further, as dimensions get smaller in the deep sub-micrometer range, it becomes increasingly difficult to define metal pillars or plugs making electrical connection between different levels of metalization.
A need remains for a process of fabricating metal pillars or plugs for making contact between metal layers.